I just remembered one more thing with the fuel injected vehicles. Does that truck have a temp sensor? I am a carb man so not familiar with what those years had in them. If it has a temp sensor, then use OBD1 system to check it. Does not always throw a code unless the system is stuck open or closed. It may be reading the incorrect temp and causing the ECM to send the incorrect fuel mixture and timing. I have seen this a couple of times.